Low Carbon Footprint Recycling of Post-Consumer PET Plastic with a Metagenomic Polyester Hydrolase.

Christian Sonnendecker,Bernd Abel,Wolfgang Zimmermann,P Konstantin Richter,Heinz‐Georg Jahnke,Paula Blázquez‐Sánchez,Patrick Hille,Norbert Sträter,Ziyue Zhao,Felipe Engelberger,Juliane Oeser,Cornelius Fischer,Holger Lippold,Yuliia Lihanova,Susan Billig,Thorsten Oeser,César A Ramírez‐Sarmiento,Jörg Matysik,Ronny Frank

doi:10.1002/cssc.202101062

Abstract

Earth is flooded with plastics and the need for sustainable recycling strategies for polymers has become increasingly urgent. Enzyme‐based hydrolysis of post‐consumer plastic is an emerging strategy for closed‐loop recycling of polyethylene terephthalate (PET). The polyester hydrolase PHL7, isolated from a compost metagenome, completely hydrolyzes amorphous PET films, releasing 91 mg of terephthalic acid per hour and mg of enzyme. Vertical scanning interferometry shows degradation rates of the PET film of 6.8 μm h−1. Structural analysis indicates the importance of leucine at position 210 for the extraordinarily high PET‐hydrolyzing activity of PHL7. Within 24 h, 0.6 mgenzyme gPET −1 completely degrades post‐consumer thermoform PET packaging in an aqueous buffer at 70 °C without any energy‐intensive pretreatments. Terephthalic acid recovered from the enzymatic hydrolysate is then used to synthesize virgin PET, demonstrating the potential of polyester hydrolases as catalysts in sustainable PET recycling processes with a low carbon footprint.

Highlights

Plastics are ubiquitous and appear to be indispensable in our daily life
Residue F243 (LCC), which is characteristically replaced by serine in IsPETase[36] and other Type IIb polyester hydrolases[37] and is replaced by L210 in PHL7, is one of the three residues that contributes most of the binding energy in LCC but has a negligible contribution towards ethylenemono-terephthalate-mono(2-hydroxyethyl terephthalate) (EMT) binding in PHL7. These results suggest that the phenylalanine/leucine replacement could be partially responsible for the changes in per-residue binding energy contributions in PHL7, to what was observed for IsPETase by the substitution of the highly conserved phenylalanine in thermophilic enzymes by serine.[36]
A degenerate primer method has shown to be useful for the isolation of novel metagenomic polyester hydrolases from plant composts

Summary

Introduction

Plastics are ubiquitous and appear to be indispensable in our daily life. Due to their manifold applications and low cost of the petrochemical building blocks, the amount of plastics has immensely increased over the past decades.

Results

Conclusion